The present invention relates to earth retaining walls, such as mechanically stabilized earth retaining walls, and particularly to anchor system for such walls.
Mechanically stabilized earth (MSE) retaining walls are construction devices used to reinforce earthen features, such as slopes, particularly where changes in elevations occur rapidly, such as site developments with steeply rising embankments. These embankments must be secured, such as by retaining walls, against collapse or failure to protect persons and property from possible injury or damage caused by the slippage or sliding of the earthen slope. For instance, MSE walls are frequently integrated into overpass and bridge embankment structures. MSE systems can have other applications, such as to support earthen features providing sound abatement for a neighborhood or commercial complex adjacent a heavily traveled road. MSE walls can also be used to support and retain earthen landscaping features.
MSE system designs must account for lateral earth and water pressures, the weight of the wall, temperature and shrinkage effects, and earthquake loads. As illustrated in FIG. 1, a typical MSE system 10 employs a wall 12 supported on a base material 18. The wall 12 is offset from retained earth or soil E which is typically at a 45° slope. Granular backfill 16 occupies the space between the wall and the retained soil. The MSE system 10 includes a plurality of anchor elements 14 projecting from the wall 12 into the backfill 16. Friction between the anchor elements 14 and granular backfill 16 hold the wall in place, which in turn holds the backfill and retained soil E in place.
In a typical MSE system, the wall 10 is formed of a plurality of modular facing units, such as precast concrete members, blocks, or panels, stacked together. The facing units may be configured to create an aesthetic visual appearance facing away from the reinforced soil. The anchor elements 14 may be either metallic or polymeric tensile reinforcements disposed in the backfill or soil mass behind the wall.
The anchor elements 14 may be fastened to or held within the wall 12 in a number of ways. In one approach, the anchor elements are fastened to a wall anchor that is embedded or trapped within the wall itself. Thus, as shown in FIG. 2, a wall anchor 20 includes a generally triangularly shaped embedded end 21 from which extends an elongated attachment end 22. The attachment end receives a clamping bolt and nut 23 that can be used to clamp one end of an anchor element 14 to the wall anchor 20. The embedded end 21 may be anchored within a concrete wall block as the block is being poured, or may be embedded within a cavity formed in adjacent stacked wall blocks. Another form of wall anchor 25 is shown in FIG. 3. This wall anchor includes a pair of legs 26 embedded within the wall 12. An elongated attachment end 27 extends from the wall 12 and includes a clamping bolt and nut 28 for attachment to an anchor element.
The standard specifications for MSE walls are based upon the strength of the interlocking components forming the wall and the load created by the backfill.
Once the desired wall height and type of ground conditions are known, the number of anchor elements 14 or tensile reinforcements, the vertical spacing between adjacent reinforcements, and the lateral positioning of the reinforcements may be determined, dependent upon the load capacity of the interlocking components. A typical anchor element is in the form of a planar wire grid spanning the width of the wall 12 and projecting a predetermined distance (i.e., 3 feet) from the wall into the backfill 16.
Heretofore, construction of such mechanically stabilized earth retaining walls has been limited to large, financially significant projects. This is due in part to the cost of the mechanical components used for construction of such earth retaining walls. To reduce costs, tensile reinforcements other than grids have been developed for use with mechanically stabilized earth retaining walls. For instance, flexible perforated reinforcement sheets have been used that are significantly less expensive, but more difficult to connect to the MSE wall.
As the demand for MSE systems increases, the need for cheaper, effective anchor elements or tensile reinforcements also increases.